Recently Google published that they will be giving a boost to companies and websites that encrypt their entire site with SSL (this is the official release). My advice is to put this on your development schedule and start working toward this goal.
Remember, you’ll need to 301 redirect your old non-secure site to the new SSL enabled site. Which means you’ll most likely take a short term hit in rankings over the migration period (but you should gain long term benefits)
Your checklist should be as follows:
– check all scripts on your site to ensure nothing is still pointing to the non secure version of your site.
– check to make sure everything works in the secure url structure.
– 301 redirect the non-secure to secure
– flip the switch to point everything to secure.
– go to webmaster tools and force complete respider of your site.
– Contact anyone possible that is linking to your site and ask them to point to https rather than http.
This is going to be a process, but at the end your site will most likely rank better in the long term.